In no particular order:

1. The owner doesn’t use content sharing services – tools like technorati, Digg, FeedBurner, Google Blogs, etc. are great ways to publicize good content.  The end result, the blogger is whistling in the wind.

2. The content isn’t unique – either the writer hasn’t developed a particular voice, or is simply providing links to other peoples content.  Thus when readers check in, they find nothing of value to bring them back.

3. Over use of advertising – it makes the blog too hard to read, and makes it appear to be more of a revenue vehicle than a communication means.  Bloggers and blog readers turn off at overt marketing pitches.

4. Dead Blog Syndrome (DBS) – the blogger updates so infrequently most readers stop checking back.  My gut is that a blog needs at least two posts a week, and one of those should probably have some new thought, the other could be simple commentary on the hot blog issues of the day.  Give readers a reason to put you in their morning reads and you’re on your way to success.

5. Knee Jerk Blogging – many bloggers feel the need to write about every hot issue of the day.  Boring…I don’t need to hear yet another viewpoint on Anna Nicole, the Ft. Dix terrorists, etc.  Chances are whatever you have to say on those issues, it’s been said somewhere else, and said better.  And unless you’re specifically blogging about politics, it’s probably a good idea to avoid topics like “Bush should be (take your pick, Sainted or Impeached)”.

Here are a couple of links on the subject (I read them after writing this…)

Bloghash – 4 Reasons Blogs Fail
BlogCut – 5 Reasons why Blogs Fail?
The Wrong Advices – Why Do Blogs Fail?

Great reading in all of them…